1. Field of the Invention
The present invention relates generally to semiconductor memories and, in particular, to a lateral phase change memory.
2. Description of the Related Art
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, as an electronic memory. One type of memory element utilizes a phase change material that is electrically switched between generally amorphous and generally crystalline local orders or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states.
Typical materials suitable for such an application include various chalcogenide elements. The state of the phase change materials is also non-volatile, absent application of excess temperatures, such as those in excess of 150° C. for extended times. When the memory is set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reprogrammed, even if power is removed. This is because the programmed value represents a phase or physical state of the material (e.g., crystalline or amorphous).
Prior art phase change memories have a vertical structure including a stack of an upper electrode, a phase change material region, and a lower electrode. Because of the presence of the intervening phase change material region and the fact that the upper electrode is formed on the phase change material region, the electrodes are made of different materials. More particularly, the top electrode is made using low temperatures to avoid adverse effects on the phase change material region when the upper electrode is deposited. However, the use of different materials for the upper and lower electrodes may result in various disadvantages.
Therefore, there is a need for better phase change memories.